Translucent mariner&#39;s compass



A. E. RITCHIE.

IRANSLUGENT MAHINER'S COMPASS. APPLICATION FILED NOV. 10, 19!?- 1,332,304. Patented Mar. 2, 1920.

ANDREW ELIQT RITCHIE, 0F BROOKLINE, MASSACHUSETTS.

TRANSLUGENT MARINERS COMPASS.

I Specification of Letters Patent.

Patented Mar. 2, 1920.

Application filed November 10, 1917. Serial No. 201.367.

To all UYILOII'I/ it may concern Be it known that I, ANDREW ELIOT llircnni, a citizen. of the United States, residing at Brookline, in the county of Norfolk and State of Massachusetts, have invented new and useful Improvements in Translucent Marinersfi Compasses, of which the following is a specification.

The presentinvention relates to compasses for marine use of the type in which a transparent or translucent bottom is provided in order that the compass card or other in dicator may be illuminated by light coming from beneath. In nautical compasses the magnetic needle or needles are attached to a card bearing thedirections, and are floated in a body ofliquid which is contained in a recepiaclc ordinarily called a bowl. v Such bowls necessarily are provided with expansion. means in order to permit the liquid, which completely fills the bowl and is hermetically sealed therein, to expand and contract with out doing injury to the bowl. My inyentiou hereafter set forth and claimed consists in the combination with expansion means for this purpose having advantageous features ot a sep: 'ator device between the expansion chamber and the interior of the bowl which .ps the compass needle alway' steady; The .ecise nature and characteristics of the in reution appear from the following description in connection with the drawings of a nautical compass having my invention applied thereto, and pointed outin the claims. In the drawings,

Figure 1 isa .cross section of a nautical compass embodying my invention.

Fig. 2 is a plan View of the same.

Fig. 3 is a cross section illustrating the invention applied to a modified form of compass.

Referring to the drawings 10 represents a compass bowl here shown as of standard construction having knife edge trunnions 11 mounted. in a standard gimbal ring 12. 13 is the compass card, 14: the magnetic needles which are attached to the card by wires 15, and 16 is a float connected to the needles for buoying up the latter'and the card in the liquid with which the bowl is filled; this float having a recess in its under side fitted with a bearing 17 to admit the pivot 18 by which the positions of the needles and card, and the center of rotation thereof, are established. Across the open top of the bowl is placed a transparent pane 19, ordinarily ofheavy glass secured by a ring 20 and a compressible but elastic gasket 21.

The bottom of the bowl is formed as an annular ledge to which is connected the expansion chamber 23, the latter being formed of two annular members connected together atone edge, preferably the outer edge, one of them connected at the opposite edge to the bottom 22, and the other connected at its correspondingedge to the ring 2-1 which mounts the bottom translucent plate or pane 25; thus providing inctlect a bellows wall. Pane 25 is conveniently secured by a ring 26 and gasket 27 in a manner similar to that in which thevpanc 19 is secured. 28 represents the usual weighted rinp; mounted under the bowl and secured thereto by arms 28 or a continuous web. said ring being; provided to keep the bowl upright, and being adapted to admit light. to the transparent bottom plate 25.

It has been found in practice that when the entrance from the bowl proper to the expansion chamber is left entirely open or unobstructed. variations and inaccuracies in the action of the compass needles occur if the bowl is suddenly moved in any direction. or shaken, these variations having the form of rapid and violent oscillations of the needle,,which make it ditficult to distinguish. the indications on the card at all, and impossible to read them accurately.

I have discovered and perfected a means of the needle and for keeping the needle steady at all times. This means is part of my invention and comprises a septum 29 which is necessarily transparent or translucent, and also insoluble in the liquid. with which the compass bowl is filled. I may use any material for this septum which has these characteristics, among others glass and mica. the latter being preferable on the whole because it is practically unbreakable and is flexible as well as translucent and insoluble. Such septum is mounted in the opening between-the bowl and the expansion chamber. A convenient means for mounting it comprises a ring having a flange which rests on and is secured to the bottom of the bowl. and an inwardly directed lip which underlies the edge of the septum. A retaining means 31 in the form of a wire hoop sprung into a I for preventing this aberration in. the act-ion groove in the ring overlies the edge of the septum. The latter has a hole 32 in its center for the double purpose of permitting displacement of the body of liquid in the bowl to and from the expansion chamber, and of permitting the pivot 18, which is secured in the center of the bottom pane 25, to extend through into the bowl.

The contraction of the opening from the bowl to the expansion chamber provided by this septum entirely corrects the error in the action of the needle heretofore described and without interfering with as free flow of the liquid as is necessary to permit the expansion chamber to perform its designed otiice. Ido not attempt to explain the reason for either the effect of vibration under certain conditions as above set forth, when the septum is absent, or of the elimination of such vibrations when'the septum is present, but content myself with the statement of the observed fact that these effects occur under re spective conditions as set forth. Considera ble variation with respect to the diameter and location of the aperture and in the number of such apertures is possible, and the same may be made considerably larger in proportion to the diameter of the compass bowl than as shown in the drawings, or placed in another location, or a number of holes having a combined area greater or less than that of the hole 32 may be made, without nullifying the efifect of the septum; but the opening, or the combined area of all the holes or openings must also be materially smaller than the diameter of the entrance to the expansion chamber.

The modification in Fig. 3 consists in so mounting the pivot that it does not pass through the septum and no part of it is contained in the expansion chamber. Here the mounting for the pivot consists of a bar 33, attached to the bottom of the bowl inside the same and crossing the entrance of the ex pansion chamber, upon which the pivot is mounted by essentially the same means as that shown in.Fig. 1 for mounting it upon signature.

the bottom pane 25. The advantage of this modification'is that it avoids perforating the bottom pane 25 and consequent need of so packing the support for the pivot that leakage will not occur, and also the danger of cracking the pane by carelessly setting up themount, in case the pane is of glass. In all other respects the compass shown in 3 is the same as shown in Fig. 1 and the parts thereof are designated by the same reference characters. I

What I claim and desire to secure by Letters Patent is:

1. A nautical compass comprising a bowl, an expansion chamber constructed to permit light to pass through it connected to the bot tom of the bowl and extensible downwardly, and a translucent septum extending across the entrance to the expansion chamber and having a relatively contracted aperture.

2. In a nautical compass, a bowl, an expansion chamber formed of two flexible rings connected together at their outer peripheries, one of which is connected at its inner periphery to the bottom of the bowl, and a transparent pane connected to the inner periphery of the other ring,and a translucent plate mounted adjacent to the junction between the bowl and the expansion chamber, extending over the entrance to the latter and having a relatively contracted opening.

3. In a transparent nautical compass, a bowl having a transparent pane mounted across its top and having an opening in its bottom, an expansion chamber formed in part of a transparent bottom pane and in part of a bellows wall connected to said pane and to the bottom of the bowl across the opening in said bottom, the bowl and expansion chamber being filled with liquid, and means partially obstructing the opening between the bowl and the expansion chain:

In testimony whereof I have afiixed my ANDREW ELror RITCHIE. 

